expectations
it's a paradoxical situation here; you need to have it and you can do without it too.
put it this way, it feels good to have people believing in you; that YOU can do it, it's like a constant pat in the back, people having faith in you. makes you really feel good about yourself. then, when you don't do well, you have the extra burden of feeling that you let these people down. so now, not only do you feel that you have let yourself down, you also have this accountability to the others that had so much faith in you. in order not to feel like crap, you put so much pressure on yourself to do well which may result in what you don't desire - failure.
there'll be other times when a little pressure you put on yourself is amplified by the faith these other people have in you. because of the desire to not want to fail them, you add more pressure on your weight-laden shoulders, then it might come to a time when you just collapse due to the immense weight you felt you had to carry.
i'm the same, i do feel good when people feel that i can do it, however it seems that i perform my best when no one seems to have any faith in me. but crap, i know some people think i'm smart, trouble is i think they overestimate my capabilities, so in order to match up to their expectations i've to work doubly or triply hard to seem THAT smart. which obviously i can't be bothered to do so, it's better that people think you're dumb and when you fare well, they'll just credit it to luck. which seems pretty fare cos luck's this enigmatic force that is not to be trifled with.